Regarding a wireless communication system providing services for CSG (Closed Subscriber Group) cells, the area of service provided by a micro base station for a CSG cell is smaller than the area of service provided by a macrocell base station. For this reason, if a mobile terminal in communication continues to move, and even if the mobile terminal once accesses the micro base station for the CSG cell, the mobile terminal moves out of the area of the service provided by the micro base station in no time, and therefore performs a handover from the micro base station for the CSG cell to the macrocell base station. Thereafter, if the mobile terminal returns to the original place, the mobile terminal performs a handover to the original micro base station for the CSG cell. If the mobile terminal moves to a new place, the mobile terminal performs a handover to a micro base station for a new CSG cell. Thus, it has been known that if the mobile terminal moves, the number of handovers increases compared to a wireless communication system of related art which provides services only for macrocells.
If a mobile terminal moves and frequently performs a handover from a macrocell base station to a microcell micro base station, or from a microcell micro base station to a macrocell base station, the amount of control data communicated between the mobile terminal and the base station increases, thereby causing a decrease in the amount of user data and therefore causing a reduction in throughput. Other than that, if a handover is repeatedly performed, a network exchanger has a heavy load to manage the positions of mobile terminals, thereby increasing the load of communication networks. For this reason, to prevent a handover from being frequently performed, there has been the following methods.
Patent Document 1 discloses a method for a mobile terminal to limit handover operation based on the remaining amount of a battery of the mobile terminal. Patent Document 2 discloses a method for a mobile terminal to detect the moving speed thereof, stop to perform a handover according to the speed, and access a macrocell.
Here, a CSG (Closed Subscriber Group) cell means a cell among microcells, which only specific users are allowed to access.